Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-05-17
2001-07-24
Ball, Michael W. (Department: 1733)
Metal working
Method of mechanical manufacture
Electrical device making
C219S121640, C429S185000
Reexamination Certificate
active
06264708
ABSTRACT:
BACKGROUND
The present invention relates to a method of manufacturing prismatic batteries, and more particularly to an improved method for hermetically sealing a prismatic case housing power generating elements by welding a sealing plate on the open end of the prismatic case.
By way of example, secondary batteries used as power sources for portable electronic instruments are required to be of a high energy density and, at the same time, are required to be of a shape efficient in terms of space used in order to achieve weight-lightness and compactness. A lithium ion secondary battery which uses a prismatic aluminum casing is a battery which fulfills these requirements.
Because the lithium ion secondary battery, in terms of its structure apart from anything else, is required to be hermetically stable over a long time, a sealing plate is bonded by laser welding to the open end of a prismatic case formed as a square tube shape with a bottom, thereby sealing its open end. Such a laser welding method has a characteristic of excellent operation efficiency as compared with other welding methods, since it causes less thermal effect on the electrolyte and electrically insulated portions housed within the casing.
Conventional methods for manufacturing prismatic batteries by laser welding of the prismatic case and sealing plate include those disclosed in Japanese Patent Laid-open No. 8-315788, Japanese Patent Laid-open No. 8-315789, and Japanese Patent Laid-open No. 8-315790. In these disclosed manufacturing methods, the sealing plate is fitted into the open end of a prismatic case, which is positioned with the open end facing upwards. The laser beam is irradiated from a vertical direction toward the abutment area of the prismatic case and sealing plate; and this abutment area is scanned with the laser beam and welded, whereby the open end of the prismatic case is hermetically sealed with the sealing plate.
However, in order to weld the abutment area between the sealing plate and the prismatic case which is disposed upright with its open end facing upwards with the laser beam that is irradiated from the vertical direction, it is necessary to move either the laser beam or the prismatic case along the welding line formed of straight lines of four sides linked by each corner at the open end of the case, wherefore control of scanning the abutment line to be welded with the laser beam becomes complex, thus causing a problem of low production efficiency. Also, since weld penetration caused by welding occurs towards the inside of the battery as the abutment area is welded by the laser beam irradiated from the vertical direction, there is a risk of molten metal infiltrating the battery if the amount of penetration is increased. Moreover, the precision to which the prismatic case and sealing plate can be finished does have limits. Even if the amount of penetration during welding is optimized so as not to reach into the battery, penetration may reach into the battery due to variations in the finishing precision of the thin materials. In such a case, molten metal dropping into the battery may cause internal short circuits. Moreover, although laser welding is a welding method which does not have much thermal influence on the electrolytic solution and electrical insulating matter, since the heating is directed towards the battery interior, thermal effects are difficult to eliminate because of limits to welding precision or to the finishing precision of the prismatic case and sealing plate.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the foregoing problems in the prior art. It is an object of the present invention to provide a method of manufacturing prismatic batteries with which control of scanning with a laser beam for performing laser welding can be simply made, and the prismatic case and sealing plate can be joined by a uniform weld and without thermal effects on the interior of the battery.
In order to accomplish above said object, the method of manufacturing a prismatic battery according to the present invention wherein power generating elements are housed in a prismatic case formed as a square tube shape with a bottom having a square opening configuration including four straight sides and curved corners of a prescribed radius, and a sealing plate is laser welded to the open end of the prismatic case, thereby sealing the open end of the prismatic case with the sealing plate. The sealing plate is abutted to the open end of the prismatic case; a laser beam is directed from a lateral direction of the prismatic case to an abutment line where the prismatic case and the sealing plate are abutted with each other; and the laser beam is moved linearly along a direction parallel to lines of the four sides, whereby the prismatic case and the sealing plate are laser welded together.
According to the above manufacturing method, the sealing plate is abutted onto the open end of the prismatic case to form at the upper end of the prismatic case, an abutment line where the sealing plate meets the open end of the prismatic case. By irradiating laser beams to this abutment line from a lateral side of the prismatic case and by scanning it along parallel to the four sides, the sealing plate is welded to the open end of the prismatic case. In this welding method, since the scanning with the laser beam is made along a straight line, the control thereof is simple.
In the above manufacturing method, by scanning each of the abutment lines at the same time with four laser beams respectively provided corresponding to each of the four sides in the directions parallel to the lines of each side, welding of all four sides is simultaneously performed. Operation efficiency is thus improved, and slippage of the sealing plate due to the welding operation does not occur.
Also, by scanning and welding each of the abutment lines successively with a pair of or a single laser beam, in parallel to lines of the four sides, a given pair of opposing abutment lines is welded at the same time, whereby slippage of the sealing plate caused by the welding operation is prevented and welding is performed efficiently. Also, if the sealing plate is securely held in position on the prismatic case, welding can be sequentially performed starting from any given one of sides by scanning with the laser beam in parallel to this side.
Furthermore, by controlling the scanning with the laser beam such as to change the laser output in accordance with a curving radius of the corners when the laser beam is moved between straight lines of each side and the corners, unevenness of the welding strength because of the difference in the focal distance of the laser beam between the straight sides and the curved 5 corners is compensated for by the variation of laser output, whereby decrease in the welding strength at the corners can be prevented.
Scanning with the laser beam may also be controlled such as to change the pulse separation of the laser beam in accordance with a curving radius of the corners when the laser beam is moved between straight lines of each side and the corners. An irradiation amount of laser beam per unit time is equalized in the straight sides and curved corners by varying the pulse separation of laser beam, whereby unevenness in the welding strength caused by difference in the focal distance of laser beam will be eliminated and decrease in the welding strength at the corners can be prevented.
Furthermore, by giving an inclination to the irradiation angle of the laser beam at a prescribed angle with respect to the direction of scanning line, the incident angle of the laser beam in relation to the corners does not become acute, whereby the decrease in welding strength at the corners can be reduced. Also, damages of the laser irradiation source caused by the reflected light of the irradiated laser beam can be eliminated.
Furthermore, prismatic cases respectively having the sealing plates placed on the open end thereof may be arranged in a row, and laser beams irradiated from a direction orthogonal to the direction o
Haraguchi Kazunori
Nakashima Takuya
Senoo Kikuo
Takeuchi Takashi
Yoshizawa Hiroshi
Ball Michael W.
Jordan and Hamburg LLP
Matsushita Electric - Industrial Co., Ltd.
Tolin Michael A.
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